Noise is emerging as both an economic and public policy issue. Soundproof rooms are required for a variety of purposes. For example, apartments, hotels and schools all require rooms with walls, ceilings and floors that minimize the transmission of sound thereby to avoid annoying people in adjacent rooms. Soundproofing is important for offices and meeting/conference rooms where speech privacy is sought. Another facet of privacy is the requirements legislated under the Health Insurance Portability and Accountability Act (HIPAA), for environments such as doctors' offices, medical examining rooms, or pharmacies. The HIPAA act requires that covered entities, such as hospitals, physician offices, and other medical treatment facilities, must implement reasonable safeguards to limit incidental eavesdropping, and avoid prohibited uses and disclosures of private patient information. These safeguards include physical facility safeguards to protect patient privacy. As a result, these medical treatment facilities may be particularly concerned with providing adequate sound transmission reduction in areas where patient information is discussed. Soundproofing is also particularly important in buildings adjacent to public transportation, such as highways, airports and railroad lines. Additional noise sources include theaters, home theaters, music practice rooms, recording studios and others. One measure of the severity of the problem is the widespread emergence of city building ordinances that specify minimum noise isolation ratings.
Various types of ceiling systems have been used in commercial and residential building construction to provide the desired acoustical performance. One popular type of ceiling system is a suspended acoustical tile ceiling, which typically comprises some sort of frame structure suspended from the structural ceiling of the room. A plurality of ceiling tiles are then supported by the frame structure, thereby creating a ceiling plenum above the ceiling tiles. This ceiling plenum may be used to provide an easily accessible space in which heating, plumbing, wiring, and other service installations may be disposed. In many conventional commercial installations, the interior walls terminate at the suspended ceiling grid face, with the ceiling plenum extending across the interior walls of the building. This creates a common cavity and a likely path for sound transmission between adjacent rooms. In one type of suspended ceiling, the frame structure comprises a grid of T-bars, which are used to support a plurality of rectangular “drop-in”-type ceiling tiles. These ceiling tiles may vary in size, but are often 2′×2′ or 2′×4′.
The American Society for Testing and Materials (ASTM) has developed test method E1414 to standardize the measurement of airborne sound attenuation between rooms sharing a common ceiling plenum. The rating derived from this measurement standard is known as the Ceiling Attenuation Class (CAC). Ceiling materials and systems having higher CAC values have a greater ability to reduce sound transmission through the ceiling plenum.
Another important characteristic for ceiling tile materials is the ability to reduce the amount of reflected sound in a room. One measurement of this ability is the Noise Reduction Coefficient (NRC) rating as described in ASTM test method C423. This rating is the average of sound absorption coefficients at four ⅓ octave bands (250, 500, 1000, and 2000 Hz), where, for example, a system having an NRC of 0.90 has about 90% of the absorbing ability of an ideal absorber. More recently, the NRC has been superseded by Sound Absorption Average (SAA), which is also governed by the ASTM C423 test method. The SAA value is the average of the sound absorption coefficients for twelve ⅓ octave bands from 200 to 2500 Hz, inclusive. For both the NRC and SAA, a higher value indicates that the material provides better sound absorption and reduced sound reflection. Within the context of this document, the terms NRC and SAA are used interchangeably and are considered generally equivalent ratings of sound absorption.
Increasing the amount of sound absorption in a room can decrease the amount of reverberation in the room. Reverberation time is the time required for the sound pressure level to decay by 60 dB after the sound source has stopped. This is an important design parameter, because a shorter reverberation time indicates a reduction of interior noise levels and increased speech intelligibility. Reverberation time is dependant upon the volume of the room and the amount of sound absorption present. The selection of the amount of sound absorption to be provided for a particular room depends upon the intended usage of the room. In commercial settings, the desired acoustical properties of a ceiling are generally balanced with a desire to minimize material and labor costs during construction. Conventional ceiling tiles are often formed by a substrate of, for example, mineral or wood fiber, with a facing material layer provided on the side exposed to the interior of the room. The mineral fiber substrate provides the primary sound absorption qualities, while the facing material layer is generally used to improve the aesthetic appearance of the ceiling tiles.
Materials having good absorption properties are often porous and allow sound to easily pass through the material, thereby resulting in high sound transmission and in poor sound attenuation. Therefore, if high sound attenuation is desired, a customer may often have to compromise on sound absorption in selecting a material for use as a ceiling panel. In some conventional ceiling tile installations, additional acoustic insulation is added above the ceiling tiles in the ceiling plenum. While this may improve aspects of the acoustic performance of the ceiling, the installation of additional insulation can dramatically increase the cost of installation and maintenance, and add bulk to the ceiling system's design. Further, the technique is a non-standard method and may lead to inconsistent results. Accordingly, there is a need for an improved and integrated system for use as a ceiling panel that provides both high sound absorption and high sound attenuation properties.